As an electromagnetic contactor, there is known a device which accommodates, in a case, an electromagnet having a movable core, a movable contact support which moves in parallel with directions of movement of the movable core (an attraction movement, a release movement), a return spring which urges the movable contact support toward its initial position, and a drive lever which transmits the movement of the movable core to the movable contact support (e.g., Patent Document 1).
A description is given of the conventional electromagnetic contactor of this type with reference to FIGS. 6 and 7. As shown in FIG. 6, an electromagnetic contactor 1 includes a lower case 3 and an upper case 4, and in the upper case 4, there are disposed a plurality of terminal portions each having a contact (reference numerals 10a to 10d in FIG. 7), and a coil terminal of an electromagnet 8 described later. The upper opening portion of the upper case 4 is covered with an arc extinguishing cover 5.
In the upper case 4, a movable contact support 7a is accommodated. The movable contact support 7a includes a movable contact support base 7a1, and a movable contact support cover 7a2 which is coupled to the movable contact support base 7a1 in a fitting manner.
As shown in FIG. 7, the movable contact support base 7a1 is formed with a plurality of partitions 13 at predetermined intervals, and movable contacts 7c1 to 7c4 are supported between the partitions 13.
The terminal portions 10a to 10d disposed in a row in the upper case 4 are provided with contact pieces 12 protruding toward the movable contact support base 7a1, a normally open fixed contact TNO is formed on one side surface of the tip of the contact piece 12 of each of the terminal portions 10a and 10b, and a normally closed fixed contact TNC is formed on the other side surface of the tip of the contact piece 12 of each of the terminal portions 10c and 10d. 
The movable contacts 7c1 and 7c2 of the movable contact support base 7a1 oppose the normally open fixed contacts TNO of the terminal portions 10a and 10b, and are urged by contact springs 14 in a direction in which the movable contacts 7c1 and 7c2 are moved away from the partitions 13. In addition, the movable contacts 7c3 and 7c4 of the movable contact support 7a1 oppose the normally closed fixed contacts TNC of the terminal portions 10c and 10d, and are urged by contact springs 15 in a direction in which the movable contacts 7c3 and 7c4 are moved away from the partitions 13.
At one end portion in a longitudinal direction of the movable contact support base 7a1, a return spring 7b is disposed, and the movable contact support 7a is urged by the urging force of the return spring 7b toward the right in FIG. 6.
In the lower case 3, an AC-operated electromagnet 8 is accommodated. The electromagnet 8 includes a coil frame 8b having an exciting coil 8a wound therearound, a fixed core 8c which is inserted into the hollow portion of the coil frame 8b and fixed to the side wall of the lower case 3, and a movable core 8d which opposes the fixed core 8c so as to be movable close to or away from the fixed core 8c and is inserted into the hollow portion of the coil frame 8b, and is disposed such that the movement directions of the movable core 8d (the attraction movement and the release movement) are in parallel with the movement direction of the movable contact support 7a. 
In addition, a drive lever 9, which transmits the attraction movement and the release movement of the movable core 8d to the movable contact support 7a, is accommodated so as to be extended between the lower case 3 and the upper case 4 in a state where the drive lever 9 is connected to the other end side of the movable contact support 7a which is apart from the return spring 7b and the movable core 8d. 
The drive lever 9 is a plate-like member. In the drive lever 9, one end thereof in a longitudinal direction is engaged with the inner wall of the arc extinguishing cover 5 to serve as a rotation shaft portion 9a, a movable core connection portion 9b formed on the other end side in the longitudinal direction is inserted into and connected to a connection hole 8e formed in the movable core 8d, and a movable contact support connection portion 9c formed in the central portion in the longitudinal direction is engageable with the other end side of the movable contact support 7a. 
When the exciting coil 8a of the electromagnet 8 is in a non-excited state, an attraction force does not act between the fixed core 8c and the movable core 8d, and the movable contact support 7a is positioned on the right in FIG. 6 by the urging force of the return spring 7b (an initial position of the movable contact support 7a). At this point, the movable contacts 7c1 and 7c2 of the movable contact support 7a are apart from the normally open fixed contacts TNO of the terminal portions 10a and 10b to serve as contacts, while the movable contacts 7c3 and 7c4 are contacting with the normally closed fixed contacts TNC of the terminal portions 10c and 10d to serve as b contacts.
When the exciting coil 8a of the electromagnet 8 is brought into an excited state, the attraction force acts between the fixed core 8c and the movable core 8d, and the movable core 8d performs the attraction movement toward the fixed core 8c. When the movable core 8d performs the attraction movement in which the movable core 8d moves to the left in FIG. 6, the drive lever 9 rotates clockwise with the rotation shaft portion 9a serving as the rotation shaft, the movable contact support 7a pushed by the movable contact support connection portion 9c moves to a contact switching position against the return spring 7b. When the movable contact support 7a has moved to the contact switching operation position, the movable contacts 7c1 and 7c2 of the movable contact support 7a contact with the normally open fixed contacts TNO of the terminal portions 10a and 10b, while the movable contacts 7c3 and 7c4 are moved away from the normally closed fixed contacts TNC of the terminal portions 10c and 10d.     Patent Document 1: Japanese Utility Model Application Publication No. H6-86245
By the way, in the conventional electromagnetic contactor 1 having the structure described above, when the movable contact support 7a shown in FIG. 6 is at the initial position, the movable core 8d of the electromagnet 8 is movable in the direction in which the movable core 8d moves close to or away from the fixed core 8c. 
As a result, in the conventional electromagnetic contactor 1, when a part of an impact force applied from the outside is transmitted as a force F which moves the movable core 8d toward the fixed core 8c, the movement of the movable core 8d is transmitted to the movable contact support 7a via the drive lever 9, and a malfunction in which the b contacts are temporarily disconnected may be caused.
As a countermeasure against the malfunction of the electromagnetic contactor 1 resulting from the impact, there may be used a structure including the return spring 7b having the urging force increased such that the movable contact support 7a does not move even when a moving force resulting from the impact is applied from the drive lever 9.
However, the countermeasure against the malfunction requires the large electromagnet 8 having a large attraction force in proportion to the return spring 7b having the increased urging force when the movable contact support 7a is moved during the normal operation, and has a problem in terms of reducing the size of the electromagnetic contactor 1.
In addition, in the conventional electromagnetic contactor 1, a malfunction in which the a contacts temporarily contact with each other by the impact force applied from the outside may occur.
As a countermeasure against such malfunction of the electromagnetic contactor 1, there may be used a structure in which the a contacts do not contact with each other even when the movable contact support 7a is moved by the impact by setting a large gap amount between the contacts of the a contacts (distance between each of the movable contacts 7c1 and 7c2 and the normally open fixed contact TNO).